1. Field of the Invention
The invention relates to a horizontal rotary hook having an outer rotating hook assembly that rotates about an axis of rotation parallel to the direction of vertical motion of the needle and, more specifically, to a horizontal rotary hook having an outer rotating hook assembly comprising an outer rotating hook body and a hook member formed of a material different from that of the outer rotating hook body.
2. Description of the Related Art
A known horizontal rotary hook disclosed in Japanese Utility Model Laid-open (Kokai) No. Sho 60-149388 has an outer rotating hook assembly comprising an outer rotating hook body formed, by molding of a resin, in the shape of a bottomed circular cylinder and a metallic hook member curved in substantially the same curvature as that of the outer circumference of the outer rotating hook body. The hook member is attached to the outer rotating hook body so as to extend along the outer circumference of the outer rotating hook body.
The extremity of the hook member is bent inward in a circular curve having a radius smaller than that of the outer circumference of the outer rotating hook body to form a thread catching part having a sharp point. An inclined loop expanding part for vertically expanding a loop of the needle thread to make the loop of the needle thread pass under the inner rotating hook assembly is formed so as to merge into the thread catching part of the hook member. When the hook member is attached to the outer rotating hook body so as to extend along the outer circumference of the latter, the thread catching part is located at a predetermined position for catching a loop of the needle thread.
Since the hook member is attached to the outer rotating hook body so as to extend along the outer circumference of the latter, the position of the thread catching part is dependent on the respective shapes of the outer rotating hook body and the hook member. Therefore, the following problems arise if the outer rotating hook body and the hook member are formed with a low dimensional accuracy. If the thread catching part is located too far from the needle, there is the possibility that the thread catching part is unable to catch a loop of the needle thread and, consequently, a stitch cannot be formed. If the thread catching part is located too close to the path of the needle or on the path of the needle, there is the possibility that the thread catching part interferes with the needle and generates noise. Accordingly, when the hook member is attached to the outer rotating hook body so as to extend along the outer circumference of the latter, the outer rotating hook body and the hook member must be formed to a high dimensional accuracy.
Although hook members can be formed at a reduced cost by bending a metal plate so that the hook members extend along the outer circumference of the outer rotating hook body, the dimensional accuracies of such hook members vary over a wide range. Therefore, it has been inappropriate to form a hook member, to be attached to the outer rotating hook body so as to extend along the outer circumference of the latter, by press-working. On the other hand, forming a hook member with a high dimensional accuracy by machining a metal blank to prevent stitch skipping and noise generation increases the cost of the outer rotating hook assembly.